I have to disagree with this. It's not that he called him a "retard". There have been plenty of times I've been out to eat or at a store, and the person working there either didn't care about the job she/he was doing and it showed or completely was out of it. I called them stupid or a retard, not to their face of course to myself/friends or w/e out of frustration. Because at the end of the day they are workers and if they don't do that job it's okay to be frustrated.. however,

The issue here really is how he treated the waiter face to face. Rolling his eyes, scoffing at the waiter, being openly rude, didn't say thank you, those things are unacceptable in my opinion. No matter how frustrated I was at customer service anywhere, I've never once been rude to the person. It might show in the tip, or I might not go back.. but there is never an excuse to be rude to a person unless they are being rude back, and even then it's best not to go overboard. That imo shows how he will be later in the relationship more so then calling someone "stupid" or a "retard".

When they get in a fight, he will roll his eyes, not appreciate what she says, think what he is saying is more important.. that is how children act, and she should def not give him another chance.